Nowadays, as an energy recovery apparatus, attention is particularly being directed to a power generator that uses a low-boiling-point medium for generating power by recovering thermal energy from a low temperature heat source which has not been utilized for conventional geothermal power generation that uses a steam turbine (see Patent Document 1).
FIG. 4 illustrates a basic system diagram of a conventional power generator that uses a low-boiling-point medium. In this power generator, heat is exchanged between a medium having a boiling point lower than that of water and a heat source through an evaporator 100 to evaporate the medium and rotate a turbine 101 by vapors from the medium, so that the resulting rotational force activates a generator 102 to obtain electric power. The medium discharged from the turbine is condensed in a second condenser 103, passed through a preheater 105 by a circulating pump 104, and then sent to the evaporator 100 again so as to repeat the above-described cycle.
In general, when a medium having a high vapor pressure (i.e., a low boiling point) is used, the medium is easily vaporized in an evaporator but has difficulty in being condensed in a condenser. To the contrary, when a medium having a low vapor pressure (i.e., a high boiling point) is used, the medium has difficulty in being vaporized but is easily condensed. In terms of turbine work efficiency, a medium that increases an enthalpy difference (heat drop) between turbine inlet and outlet to the extent possible is selected as a medium to be used. For example, as a natural medium to be used at a geothermal heat source temperature of 130° C. to 140° C. and at a cooling source temperature of 15° C. to 30° C., n-pentane (nC5H12) is mainly utilized.
Circulating cooling water or the atmosphere is a common cooling source for a condenser, and therefore, a temperature of the cooling source is widely varied between winter and summer. Hence, when a condenser is designed based only on cooling performance required in summertime, cooling performance of the condenser is further enhanced upon reduction in cooling source temperature in wintertime.
However, as illustrated in FIG. 3, a vapor pressure of n-pentane is 101 kPa or less at a temperature of 36° C. or less, and therefore, a pressure of a medium passage might be equal to or lower than atmospheric pressure when a temperature of a condenser outlet is 36° C. or less in wintertime. In that case, air might be mixed into the medium passage from a condenser main body, various joints of its connection piping or a mechanical seal portion of a turbine shaft. Such air intrusion increases a turbine outlet pressure, resulting in a reduction in efficiency.
Therefore, devices disclosed in Patent Documents 2 to 6 are each known as a device for removing air mixed into a medium in an apparatus related to power generation.
Patent Document 2 discloses a binary power generator that uses water instead of a low-boiling-point medium and includes an air extracting device for extracting air from water discharged from a condenser.
Patent Document 3 discloses a power system including a power cycle circuit through which a working fluid provided by mixing a high-boiling-point medium with a low-boiling-point medium circulates in the following order: a steam generator for generating steam by heating a solution of the working fluid; a steam turbine driven by the steam supplied from the steam generator; a condenser for condensing steam, discharged from the steam turbine, into a solution by cooling the steam; and a supply pump for supplying, to the steam generator, the solution supplied from the condenser, wherein a concentration of the low-boiling-point medium in the working fluid in the condenser is decided so that a minimum pressure which can be caused in the condenser in the power cycle circuit is brought close to atmospheric pressure.
Patent Document 4 discloses a device including: a chamber including a piston therein and located above a condenser; a valve through which the condenser and space of the chamber located below the piston are connected to each other; a cooling means for cooling, via a wall, a lower portion of the chamber with a coolant; and a discharge valve connected to the lower portion of the chamber.
Patent Documents 5 and 6 each disclose a device including: an enclosed chamber located above a condenser; a movable diaphragm which is provided in the chamber and by which inside of the chamber is divided into an upper portion and a lower portion; two flow control valves disposed in series between the condenser and the lower portion of the chamber; a cooling means for cooling, via a wall, the lower portion of the chamber with a coolant; and a discharge valve connected to the lower portion of the chamber.
Patent Document 7 discloses an organic vapor-containing exhaust gas processing method including: compressing and cooling, using a compressor and a cooler, a condensable organic vapor-containing gas from a supply line, thus liquefying and recovering organic vapors; guiding a non-condensable gas, which remains in a compressed and cooled state, to a gas separation membrane module to separate the gas into an organic vapor concentrated gas and an organic vapor diluted gas; returning the organic vapor concentrated gas to the supply line and discharging the organic vapor diluted gas while measuring an organic vapor concentration in the organic vapor diluted gas; and controlling, in accordance with the organic vapor concentration, a compression pressure applied by the compressor or a cooling temperature provided by the cooler.
Patent Documents 8, 9 and 10 each disclose an example of using a silicone rubber-based polyimide composite membrane as a gas separation membrane module for allowing organic vapors to permeate through a membrane so as to concentrate and recover the organic vapors.
Patent Document 9 discloses an organic vapor-containing exhaust gas processing method including: pressurizing an organic vapor-containing exhaust gas by a compressor and guiding the gas to a cooler; condensing and recovering organic vapors in the cooler; guiding a low concentration gas, which has been obtained after the organic vapor recovery, to a gas separation membrane module to perform a separation process; and returning an organic vapor concentrated gas to an inlet side of the compressor and discharging an organic vapor diluted gas into the atmosphere.
Patent Document 10 discloses an organic solvent vapor recovering and processing method including: supplying an organic solvent vapor-containing mixture gas to a selectively permeable membrane module through which the gas permeates and concentrates; and cooling and condensing the concentrated gas to recover an organic solvent in the liquid phase, wherein the method includes: increasing an organic solvent concentration in a non-condensable gas in the cooling and condensing step so that this organic solvent concentration is higher than an organic solvent concentration in a non-permeable gas in the membrane module; returning the non-condensable gas to a supply side for the mixture gas; and discharging the non-permeable gas in the membrane module.